In a machine tool, conventionally, moving positions of a tool and a workpiece are feedback controlled. As an example thereof, for example, there is a machine tool as disclosed in the Japanese Unexamined Patent Application Publication No. 2008-114322.
This machine tool has a base, a table which is provided on the base to be movable in an X-axis direction being a horizontal direction and to which a workpiece is mounted, a column which is provided on the base to be movable in a Z-axis direction being a horizontal direction perpendicular to the X-axis direction, a spindle head which is provided on the column to be movable in a Y-axis direction being the vertical direction, a spindle which is supported by the spindle head and to which a tool is mounted, an X-axis feed mechanism for moving the table in the X-axis direction using an X-axis motor, a Z-axis feed mechanism for moving the column in the Z-axis direction using a Z-axis motor, a Y-axis feed mechanism for moving the spindle head in the Y-axis direction using a Y-axis motor, an X-axis position detector for detecting the position of the table in the X-axis direction, a Z-axis position detector for detecting the position of the column in the Z-axis direction, a Y-axis position detector for detecting the position of the spindle head in the Y-axis direction, and a controller for feedback controlling the X-axis, Z-axis and Y-axis feed mechanisms on the basis of target moving positions of the table, column and spindle head in the X-axis, Z-axis and Y-axis directions respectively and the positions thereof detected by the X-axis, Z-axis and Y-axis position detectors, and moving the table, the column and the spindle head to their respective target moving positions.
The X-axis position detector comprises an X-axis scale having graduations In the X-axis direction and an X-axis reader for reading the graduations of the X-axis scale, the Z-axis position detector comprises a Z-axis scale having graduations in the Z-axis direction and a Z-axis reader for reading the graduations of the Z-axis scale, and the Y-axis position detector comprises a Y-axis scale having graduations in the Y-axis direction and a Y-axis reader for reading the graduations of the Y-axis scale. The X-axis and Z-axis scales are provided on the base and the Y-axis scale is provided on the column, and the X-axis, Z-axis and Y-axis readers are provided on the table, the column and the spindle head, respectively.